<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
  
  .box{
    background-color: #f00; /* #ff0000=> rgb(255,0,0) */
    color: aliceblue;
    /* text-align */
    /* 四种基本对齐方式 */
    text-align:center;
  }
  
  </style>
</head>
<body>
  <div class="box">我是div元素</div> <!--div元素独占一行-->
  
</body>
</html>